Chevron Techron Concentrate Plus (plus part is important)

LubroMoly Ventril Sauber (German made and used by VW, BMW and Porsche)

Gumout Regane (only the honey colored stuff in the clear plastic bottle, not the many other Gumouts)

Yamaha Ringfree

Redline SI-1

all seem to work fairly well

this older Motor Age magazine article is one of the better discussion of the subject:

http://web.archive.org/web/20000818062832/http://www.motorage.com/edindex/0600pg032.htm